1. Field of the Invention
The invention relates to a semiconductor memory device, and particularly to a semiconductor memory device capable of selecting data strobe types according to an operating mode.
2. Description of the Related Art
A semiconductor memory device needs to be used for various operating modes that have different strobe types. Conventionally, circuit designers design a semiconductor memory device differently according to a data strobe type. Because a semiconductor memory device with the same function is designed differently according to the data strobe type, the cost of designing the semiconductor memory device is high.
FIG. 1 is a schematic diagram showing the data transmission of a bilateral strobe type between a memory device and a memory controller, and FIG. 2 is a schematic diagram showing the data transmission of a unilateral strobe type between the memory device and the memory controller.
Referring to FIG. 1, a memory device 10 includes an upper memory 11 and a lower memory 13. The upper memory 11 transmits data to a memory controller 20 and receives data from the memory controller 20 through the channel UDQS of a bilateral strobe type. The lower memory 13 transmits data to the memory controller 20 and receives data from the memory controller 20 through the channel LDQS of the bilateral strobe type.
Referring to FIG. 2, the upper memory 11 and the lower memory 13 receive data from the memory controller 20 through an input channel DS, and the upper memory 11 and the lower memory 13 transmit data to the memory controller 20 through an output channel QS.
A semiconductor memory device uses bit organizations. For example, a bit organization of a semiconductor memory device of 16 Mbit×8 is referred to as a bit organization of X8, and a bit organization of a semiconductor memory device of 4 Mbit×16 is referred to as a bit organization of X16. The bit organization X8 represents that 8 bits of data may be input and/or output simultaneously using 8 pins.
In the semiconductor memory devices that are used today, the semiconductor memory device using a bit organization of X8 and the semiconductor memory device using a bit organization of X16 are a bilateral strobe type. In other words, the semiconductor memory devices using the organizations of X8 or X16 have a pin structure DQS through which the data may be inputted and outputted. The semiconductor memory device using a bit organization of X9, the semiconductor memory device using a bit organization of X18, and the semiconductor memory device using a bit organization of X36 are a unilateral strobe type. In other words, the semiconductor memory devices using the organizations of X9, X18, or X36 have a pin structure DS through which the data may be only inputted or have a pin structure QS through which the data may be only outputted.
Accordingly, there is a need for a semiconductor memory device capable of transmitting both the bilateral strobe type data and the unilateral strobe type data.